GB926958A - Improvements in apparatus for heating substances and objects by means of micro-waves - Google Patents

Abstract

926,958. Micro-wave heating. MIWAG MIKROWELLEN A.G. Dec. 10, 1958 [Dec. 10, 1957; April 26, 1958], No. 39880/58. Class 39 (3). Apparatus for producing a substantially even or other distribution of heating of objects or substances such as foodstuffs exposed to a microwave field within a chamber 4 containing a stand 5, e.g. of glass, for supporting the objects or substances 6 and having a door 7, microwave energy from a source 2, such as a magnetron, being radiated from a hollow waveguide 1 extending over substantially the entire surface of a slotted boundary wall 10, is characterized in that the wall 10 is constituted by a plate containing a plurality of slots 9, the plate being spaced from the walls 3 of the chamber 4 by long slots 12. The slots 9 in the plate 10 are of length about half the wavelength of the microwave energy and are distributed over the whole or a substantial portion of the plate. and their number, position and width are chosen to produce a desired pattern of micro-wave field in the chamber 4. The slots 12 can be of different width, and radiation through one or more slots 12 can be adjusted by a capacitive impedance formed by an edge 14 of the plate 10 being bent over along the slot at right angles to the plane of the plate. The bottom wall 16, Fig. 2, of the chamber 4 can be in the form of a trough the depth of which is greater than one quarter wavelength of the micro-wave energy and which is covered by a plate 17, preferably in several pieces, of low-loss insulating material, such as non-laminated opal safety glass, for supporting the objects or substances 6. The slotted plate 10 can swing through about Π(10 to 15) degrees about a horizontal axis 15 with a periodic time small in relation to the duration of heating. A trough-shaped projection 19 is provided in one vertical wall of the chamber 4 and is closed by a flap 21 pivoted at 20. In the construction shown in Fig. 3 the slotted plate and movable flap are combined in one angle-piece 22 pivoted at 23. In the constructions shown in Figs. 2 and 3 infra-red radiators 8 are provided, the movable slotted plate and flap forming reflectors for the rays. Also in the constructions shown in Figs. 2 and 3 that part of the waveguide 1 which contains the source 2 of micro-wave energy is separated from the remaining part by a vapour-tight partition 18 of an insulating material having a low dielectric constant and a small phase angle, such as a ceramic or a glass, for protecting the source 2 from vapours from the object or substances 6.